The swoop, The Sunday Times reported the next day, was "aimed at preventing subversives from establishing a 'Communist Cuba' in Singapore and mounting violence just before Malaysia".

These arrests shattered the underground communist network throughout the island.

The threat lingered, but as it faded over the years, many of those detained were released and went on to lead quiet lives.

In recent years, some have sought to give their version of events. As the 50th anniversary of Coldstore approached, several former detainees and academics began working on a book on their perspective on the detentions.

In The 1963 Operation Coldstore In Singapore: Commemorating 50 Years, launched in late 2013, they argued that the arrests were politically motivated against the leftist opposition and overstated the security threat.

Other articles and commentaries have also surfaced. Former Coldstore detainee Poh Soo Kai, a Barisan assistant secretary-general, argued last December that the purpose of Coldstore "was to eliminate Lim Chin Siong and the Barisan Sosialis from the 1963 general election".

In a feisty response to Dr Poh, the Government reiterated its position that Barisan was the main vehicle of the Communist United Front (CUF). The Barisan was formed by left-wing members who broke away from the People's Action Party (PAP) in 1961.

A new book launched this month also challenges several of these "revisionist" accounts of the communist threat head-on.

In "Original Sin"? Revising The Revisionist Critique Of The 1963 Operation Coldstore In Singapore, historian Kumar Ramakrishna rebuts three broad claims made by those who argue Coldstore was politically motivated.

These are: that the communist threat had been neutralised by the 1960s, that Barisan Sosialis leader Lim Chin Siong was not a communist or a security threat, and that Coldstore had been mounted to get rid of the progressive left.

Insight looks at these arguments and the rebuttals, and what shape the debate might take.

Was there a credible communist threat in the 1960s?

THE Communist Party of Malaya (CPM) was formed in 1930 and began establishing links with labour unions in Singapore and Malaya. During the Japanese invasion and occupation from 1941 to 1945, it was a key armed resistance force.

But after the CPM launched an armed insurgency in 1948, the Malayan government declared an Emergency, arresting leading CPM members and declaring the CPM illegal.

The CPM in Malaya was driven underground. But it embarked on a brutal campaign that took thousands of lives and drew a backlash from the authorities.

The failure of its jungle war in Malaya revived interest in urban struggle in Singapore, and official accounts show the CPM reviving its "united front" strategy of subverting trade unions and student bodies, as well as political parties like the PAP, with the long-term goal of a communist Singapore, and then Malaya.

However, Dr Poh argued that the CPM was "a decimated force in Singapore by the 1950s", largely due to the Malayan Emergency, and as a result wielded little influence over everyday events in Singapore.

Several historians described as "revisionists" have also said the scale of the communist threat was exaggerated by the authorities.

Historian Thum Ping Tjin went a step further to say that the "historiography is clear on the lack of evidence of a communist threat".

They argue that much of the left-wing radicalism - whether of students or trade unions - in that period was uncoordinated, and was more reflective of the general anti-colonial mood at the time, rather than the subversive hand of communism.

Such a view is problematic, says Associate Professor Kumar, who is head of policy studies at the S. Rajaratnam School of International Studies. He points out that the revisionists have ignored the writings of leading CPM members like Chin Peng and Fong Chong Pik, who have acknowledged their role in the CUF.

In his book, Dr Kumar argues that the communists did not resort to open, armed revolution in Singapore not out of principle, but because they could not match the strength of the British.

Instead, they adopted the CUF strategy of "peaceful struggle" by infiltrating legal organisations such as student unions and trade unions, gaining significant ground in Singapore in the 1950s.

The goal, in the words of long-time CPM secretary-general Chin Peng, was to fan hatred towards the government and undermine public order by "skilful exploitation of controversial issues and public grievances, genuine or otherwise".

These include orchestrating riots against national service in 1954, and the Hock Lee bus riots of May 1955, which saw four dead and 31 injured.

Retaliatory strikes by student and trade unions in 1956 to protest against the Lim Yew Hock government's crackdown on CUF organisations also culminated in riots that led to 13 deaths and 123 being injured. The widespread violence saw two schools burned down, 70 cars destroyed and two police stations damaged.

This led to the banning of both the Singapore Factory and Shop Workers' Union and its student equivalent, the Singapore Chinese Middle School Students' Union, and the CPM changing tack to focus on penetrating grassroots organisations and the PAP, which was founded in 1954.

The communists then attempted to seize control of the PAP in 1957, when they won six of the 12 seats on the central executive committee. They also withdrew their support in the Hong Lim and Anson by-elections in 1961, both of which the PAP lost.

These attempts, Dr Kumar says, showed a CUF determined to capture power in Singapore through constitutional means after violence failed: first with non-communists like Mr Lee Kuan Yew as cover, and then later through the Barisan, having hollowed out the PAP through defections when the marriage of convenience became untenable.

This series of events, he adds, demonstrated the CUF's nature as a "resilient, clandestine subversive organisation"."The CUF was all too real an entity in Singapore from the 1940s to the 1960s."

Associate Professor Bilveer Singh, who has written a book charting the history of communism in Malaya and Singapore, also points out that the communist threat here continued even after Operation Coldstore, with 22 incidents of arson and 11 bombings between 1969 and 1976.

He wrote in Quest For Political Power - Communist Subversion And Militancy In Singapore: "The various plots and acts of violence should debunk the notion that Singapore was not a military target, and refute claims that the communists did not do very much in Singapore."